Commander Riker is second in command of the flagship of the federation. At least one. A month he is involved in something big and huge. When he says commander Riker it means something.you might have focused too hard on the specific phrasing of 'military rank' i just couldn't think of a more apropriate term, what i meant was that your name carries weight, people have heard of your deeds and know what you do, you yourself have some level of inherent authority just because of who you are rather than any official designations, think of how the rank and file soldiers followed gandalf's orders in the battle of whitecastle, he wasn't their official leader but he could take command of them because he obviously knew what he was doing in battle, leaders took time out of business to meet him because when gandalf advises you listen to him.
Commander Sisco commands the station at the work hole. He has stopped life ending threats less than the flag ship but he is newer to command. When he says commander Sisco it mean something.
Captian Jellico out ranks then both, but no one has ever heard of him (if you know you know #Jelliciowasright)
Being in the spot light and having y the same thing.